elf: Ignore PT_PAX_FLAGS

Fixed the following abort when build was running mkzfs.py.

Done!
eth0: ethernet address: 52:54:0:12:34:56
[I/20 dhcp]: Waiting for IP...
[I/26 dhcp]: Server acknowledged IP for interface eth0
[I/26 dhcp]: Configuring eth0: ip 192.168.122.15 subnet mask 255.255.255.0
gateway 192.168.122.1
Aborted

Signed-off-by: David Leifker <dlei...@gmail.com>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>